Abstract 1689: CRISPR functional genetic screening for immune enhancers of inhibitor receptors in human primary CD8 T cells

Abstract The restrained efficacy of T cell therapies in cancer treatment is associated with T cell exhaustion (TEX), an impaired effector function state that is marked by distinct epigenetic landscape. These unique epigenetic features promoted the progression of TEX, hindered reinvigoration of TEX state and controlled the abnormal expression of inhibitor receptors (IRs), which could serve as target sites in cancer treatment. Thus, deciphering the regulatory elements in primary human T cells will deeply reveal the mechanism controlling TEX and provide novel therapeutic strategies to promote clinical response. However, how enhancers can be effectively applied in anti-cancer treatment is still poorly understood because high throughput identifying the functional enhancers of inhibitor receptors at scale is technically limited in human T cells. Here, we first developed a pooled screening platform that employs a compact CRISPRi system and enabled efficient one-step delivery of pooled screening libraries to primary human T cells. Leveraging this platform, we screened large genomic regions (~300kb) at saturation around key TEX genes, two IRs—PDCD1, HAVCR2 and one transcription factor (TF)—TBX21 to interrogate functional enhancers in human primary CD8 T cells. We identified two enhancers for PDCD1, three enhancers for HAVCR2 and three enhancers for TBX21, all of which are located over 12kb away from each gene’s transcription start sites. Then, to parse the essential sequences that fulfill enhancer function, we employed Cas9-based in-situ saturation mutagenesis screening to the identified enhancers of PDCD1 and HAVCR2. We found disrupt essential sequences impaired the entire enhancer function, quantitatively phenocopied the effect of targeting the entire enhancer with CRISPRi. Transcription factor motifs analyses of these sequences revealed potential regulation of ZFX for controlling PDCD1 expression and STAT for HAVCR2 expression. Finally, we explored the functional consequences of applying enhancers to anti-cancer treatment. Indeed, targeting the identified enhancers of PDCD1 and HAVCR2 in CAR T cells lead to enhanced cancer cell killing efficiency in vitro. Together, our study provides a platform and paradigm to interrogate functional enhancers in human T cells, illuminated the great potential of manipulating enhancers in T cell therapies. Citation Format: Ping Wang, Josephine R. Giles, Hua Huang, Junwei Shi, E.John Wherry. CRISPR functional genetic screening for immune enhancers of inhibitor receptors in human primary CD8 T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1689.